The seven-time major winner spent more than 48 hours agonizing over whether she'd be ready for the third round of the Australian Open. She decided to play, hoping enough adrenalin would kick in to allow her to get through the pain.

Williams, the No. 4 seed, was ailing after her second-round victory, her ability to move restricted by a injured right hip flexor muscle. Waiting for her in the third round was 30th-seeded Andrea Petkovic. Williams took the court on a cool Friday night at Rod Laver Arena "just hoping for some magic."

The match was over almost before it began. Williams won just one of the seven points she played before she bent over in pain, clutching her right side.

"A lot of times when you play … you get this adrenalin that blocks pain," she said. "But I just didn't get enough of that today."

The lunge to her right side on the last point aggravated a muscle in her hip that she hurt Wednesday against Sandra Zahlavova.

"I've never had to retire from a Grand Slam, especially after working so hard to pull out the match the other day," Williams said. " … It's super disappointing because this is just not how I envisioned my Australian Open being."

Williams hasn't won a major since Wimbledon in 2008. She's never won the Australian title, her best finish a runnerup to her sister, Serena, in 2003.

Meanwhile, second-seeded Vera Zvonareva kept alive her bid for a third consecutive Grand Slam final early today with a 6-3, 7-6 (11-9) win over Lucie Safarova. Zvonareva served for the match twice but was extended to the tiebreaker. Safarova led 4-2 and 5-3 in the tiebreaker before Zvona­reva finally sealed it.

And No. 4 Robin Soderling, who beat Jan Hernych 6-3, 6-1, 6-4, hasn't dropped a set and is on an eight-match win streak.

"There's always going to be a lot of attention on Roger and (Rafael Nadal), of course," he said. "But I think there's many guys who can actually compete against them and have a chance to win the tournaments like this."